DISSECTION OF THE BACK 45 



the head and neck, as they cross the posterior triangle of the 

 neck. The branches from the cervical plexus come from the 

 third and fourth cervical nerves. On the deep surface of the 

 trapezius they join with branches of the accessory nerve to 

 form the subtrapezial plexus, from which twigs proceed into the 

 substance of the muscle. The terminal twig of the accessory 

 nerve can be traced nearly to the lower margin of the 

 trapezius. 



The ascending branch of the transverse cervical artery, which 

 accompanies the accessory nerve, must be followed to the 

 anterior border of the trapezius, where it will be seen to 

 spring from the trunk of the artery. 



Dissection. The posterior belly of the omo-hyoid, the transverse 

 scapular artery, and suprascapular nerve can now be displayed by dis- 

 secting towards the upper margin of the scapula, and removing carefully, 

 the loose fatty tissue in this locality. The dissector of the head and neck 

 must take part in this dissection. 



M. Omo-hyoideus. -Arteria Transversa Scapulae (O.T. 

 Suprascapular Artery) and N. Suprascapularis (Supra- 

 scapular Nerve). The slender posterior belly of the omo-hyoid 

 muscle will be seen to arise from the upper border of the 

 scapula immediately medial to the incisura scapulae. It also 

 derives fibres from the ligament which bridges across this 

 notch. It is supplied by a twig from the ansa hypoglossi. The 

 transverse scapular artery will be noticed to enter the supra- 

 spinous fossa of the scapula by passing over the superior 

 transverse scapular ligament, whilst the suprascapular nerve 

 proceeds into the fossa under cover of that ligament. 



Dissection. Draw the scapula well over the edge of the block which 

 supports the thorax of the subject. The two rhomboid muscles are thus 

 rendered tense, and the cleaning of their fleshy fasciculi greatly facilitated. 

 The dorsalis scapuke nerve should be secured at this stage, so that it may 

 be preserved from injury in the further dissection of the region. It can 

 best be detected by dissecting in the interval between the rhomboideus 

 minor and the levator scapulae about one inch to the medial side of the 

 medial angle of the scapula (Fig. 17, p. 39). It is accompanied by the 

 descending branch of the transverse cervical artery, and it will afterwards 

 be traced upon the deep surface of the rhomboid muscles when they are 

 reflected. 



Mm. Rhomboidei. The two rhomboid muscles constitute 

 a thin quadrangular sheet of muscular fibres, which proceeds 

 from the spinous processes of the vertebrae to the base of the 

 scapula. 



